Optical projection lithography is a high resolution technique currently used for defining circuits in the semiconductor industry. As pattern resolution requirements become ever more demanding, conventional optical projection lithography is unable to meet the aggressive resolution targets required for future generation products. Parallel development is underway to enhance traditional optical projection lithography, for example, using immersion schemes, as well as to explore alternative shorter wavelength radiation sources that may provide higher resolution patterning such as extreme ultra-violet (EUV), as well as electron or ion beam based schemes and, to a certain degree, x-ray radiation.
Before advanced manufacturing lithographic tools become widely available, hybrid lithography, i.e., using a combination of different techniques such as optical lithography and direct write electron beam (e-beam) lithography for patterning one mask level, provides a viable approach to fabricate high performance devices, or for Application Specific Integrated Circuits (ASIC's). Direct write e-beam lithography is well established as a high resolution patterning technique with demonstrated resolutions below about 10 nm. However, its throughput is limited due to the serial nature of the patterning and high vacuum requirement. To reduce the write load on the e-beam tool, optical lithography is used to define patterns with less stringent resolution or alignment requirements.
It is desirable to perform both exposures in the same chemical resist layer because the pattern transfer can then be done in a single step. However, the single chemical resist use in the process must be sensitive to both radiation sources, for example, photon and electron exposure. A need exists for an improved method to allow for resist process optimization to achieve desired pattern resolutions in both lithography patterning steps.